History: White Phong part 3 - JaJDoo Shader Guide - Basics
Preview of version: 6
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I’M BLINDED!
Or
Other types of light
Table of contents
“Point me to the right direction…”
Other than point lights, we have two other types of lights in OGRE:
- Directional lights: have no position, only a direction.
- Spotlights: these lights have a ‘corridor cone’ in a direction. They have two cones:
- Inner cone: maximum illumination.
- Outer cone: gradually fading illumination.
Directional lights
These lights are probably the easiest thing in the world to calculate. All they have is a direction from which they are coming from (as if originating from infinity and traveling parallel).
All you have to do is ignore the position. That means we have one less calculation. There isn’t much more to tell, just show you the code (even that is redundant)
vertexOut mainVS(vertexIn input) { vertexOut output = (vertexOut)0; float4 worldPos = mul(input.pos, world_m); //fill output //------------------------------ output.pos = mul(input.pos, worldViewProj_m); output.normal = mul(input.normal, world_m); output.viewDir = viewPos - worldPos; //------------------------------ return output; } float4 mainPS(vertexOut input) : COLOR { //normalize per pixel //------------------------------ float3 normal = normalize(input.normal); float3 viewDir = normalize(input.viewDir); //------------------------------ //diff and specular //------------------------------ float dotNL = dot(lightPos.xyz, normal); float4 diff = saturate(dotNL); float3 halfAng = normalize(viewDir + lightPos.xyz); float dotNH = dot(normal, halfAng); float spec = pow(saturate(dotNH),50); //------------------------------ return (diff * diffColor + spec*specColor + ambientColor); }
Spotlights
Spot lights are a bit more complicated, since they originate from a specific point, project to a specific direction, and have a cone which only in it the object is affected (like a flash light). These points make it somewhat trickier.
Let’s take a look at the spotlight:
To avoid confusion, we will rename lightDir to pixelToLight since the spotlight has a facing direction.
We will use two dot products:
- dotNL : dot between pixelToLight and the surface normal
- dotPLd: dot between the inverse pixelToLight and spotlight direction
We have a few more variables however; when you ask for spotlight_params from OGRE material script, OGRE will send a float4 organized as such:
- cos(innerConeAngle/2)
- cos(outerConeAngle/2)
- falloff value
- 1
The forth value (w component) is used to help differentiate spotlights from point lights.
The cosine uses the half of the angle because the angle defines the cone, and we need only the angle between the side of the cone and the axis (which is the spotlight facing vector).
Calculating
There are two parts for determining the effect of the cone of light on the object depending on its direction to it:
- The dotNL must be positive: because otherwise we are either behind the light or on the other side of the object.
- The dotPLd value:
- The value of the dotPLd equals in value to the orthogonal to the spotlight facing vector that extends to the pixelToLight; thus, its value will determine the where is the pixel compared to the cones.
- Diffuse:
- Larger than cos(innerConeAngle/2): the pixel is in the inner cone.
- Value: the diffuse will equal the dotNL.
- Larger than cos(innerConeAngle/2): the pixel is in the outer cone.
- Value: the diffuse will equal the dotNL, multiplied by the relative location of the pixel between the outer and inner cone (will be explained later)
- Otherwise: not in the spotlight’s AOE.
- Larger than cos(innerConeAngle/2): the pixel is in the inner cone.
- Specular:
- As long as the dotPLd is positive, the specular is present; this is because the specular reflects the source of the light, which means that as long as pixel is not behind the source of the light, the specular will appear.
I ignore the falloff value, because I don’t really know what to do with it.
Code
The vertex program remained almost unchanged, but take a look at it anyhow:
vertexOut mainVS(vertexIn input) { vertexOut output = (vertexOut)0; float4 worldPos = mul(input.pos, world_m); //fill output //------------------------------ output.pos = mul(input.pos, worldViewProj_m); output.normal = mul(input.normal, world_m); output.pixelToLight = lightPos - worldPos; output.viewDir = viewPos - worldPos; //------------------------------ return output; }
The main change is in the pixel program:
We begin the program by normalizing and preparing the dot products:
float4 mainPS(vertexOut input) : COLOR { //prep //------------------------------ float3 normal = normalize(input.normal); float3 pixelToLight = normalize(input.pixelToLight); float3 viewDir = normalize(input.viewDir); float dotPLd = dot(-pixelToLight, spotLightDir); float dotNL = dot(pixelToLight, normal); //------------------------------
Now, let’s add the diffuse and specular as we described earlier and return the value:
// lights //------ float4 diff = 0, spec = 0; if(dotNL > 0) { //diffuse //------------------------------ if ( dotPLd > spotLightParams.x ) diff = dotNL; else if ( dotPLd > spotLightParams.y ) diff = dotNL * (1-(spotLightParams.x - dotPLd)/(spotLightParams.x - spotLightParams.y)); //------------------------------ // specular //------------------------------ if (dotPLd > 0) { float3 halfAng = normalize(viewDir + pixelToLight); float dotNH = dot(normal, halfAng); spec = pow(saturate(dotNH),100); } //------------------------------ } //------ return (diff * diffColor + spec*specColor);// * luminosity; }
Outer cone diffuse explained
Why
dotNL * (1-(spotLightParams.x - dotPLd)/(spotLightParams.x - spotLightParams.y));
You ask?
We need to know where the pixel is between the inner and outer cones, but in a relative value (range of 0 to 1).
Therefore, we must first do this:
spotLightParams.x – dotPLd
This will give us the absolute difference between the dotPLd (the orthogonal to pixelToLight) and the inner cone limit.
In order to receive a relative value, we divide it by the absolute difference between the inner cone limit and the outer cone limit:
(spotLightParams.x - dotPLd)/(spotLightParams.x - spotLightParams.y)
The problem is that the value is inversed (closest will equal 0) so we need to one minus it:
(1-(spotLightParams.x - dotPLd)/(spotLightParams.x - spotLightParams.y))
And finally, we need to address the angle towards the source of the light (dotNL):
dotNL * (1-(spotLightParams.x - dotPLd)/(spotLightParams.x - spotLightParams.y))
Differentiating light type
When you ask for light data from OGRE material script, you will receive all lights depending on distance, therefore, you don’t know if it’s a point light, a directional light or a spotlight.
In order to address all three in one shader, we need to know how to differ them; we need three things from the material script:
- Light_position_array
- light_direction_array
- spotlight_params
Each type of light has a different signature (a different combination of values):
Point light:
- light_position : (pos.x, pos.y, pos.z, 1)
- light_direction : not relavent
- spotlight_params : (1, 0, 0, 1)
Directional light:
- light_position : (-dir.x, -dir.y,-dir.z, 0)
- light_direction : not relavent
- spotlight_params : (1, 0, 0, 1)
Spotlight:
- light_position : (pos.x, pos.y, pos.z, 1)
- light_direction : (dir.x, dir.y, dir.z )
- spotlight_params : (cos(innerAngle/2) , cos(outerAngle/2) , falloff, 1)
“Why is light_direction not relevant in directional light?”
Because it is deprecated for greater flexibility. Instead, its inverse direction is sent in light_position (because we usually use the pixel to light)
The only reason it’s not deprecated in spotlights is that they have both direction and position.
Completionist
As a closing note, lets write a shader that an handle multiple lights of any type!
Try and write it on your own, and don’t give up – it will take a while.
Tips:
- efficiency is key : try and avoid unnecessary work
- Delegate: write sub programs to do the main bulk of the code separately, and leave the work flow in the main program.
- Shader model 3: if the program gets really branched and the work flow isn’t constant, you might have to use ps_3_0 and vs_3_0.
- Work slowly: do each task at a time; expand on need – make sure what you already wrote works.
My solution
I wrote my own version for this; it’s a bit more mature than what we wrote up to this point, but all of its elements should be familiar to you. Just follow the work flow line by line (starting with the main programs) and you’ll get it.
A few words about it:
- all positions and directions in object space, saving time (spent on transforming before calculating directional vector) and also helps result accuracy.
- Use of shader model 3.
- Use of inout for the sub programs to make them as seamless with the main program as possible.
- use of light_distance_object_space instead of manual calculation (trading attenuation accuracy for speed)
- its currently set to receive 3 light and use 3 lights. you can change the number of received lights and set a different the value for the lightCount #define with out any slowdown - the program is set only to receive that many lights in its arrays- all additional data will be discarded; as long as the lightCount is lower than the number of lights you are requesting there will no error.
- it is also set to skip all computations when receiving an empty light (if the object is affected by less than 'lightCount' amount of lights.
- It’s elegant, and I really like staring and the code.
material:
vertex_program lightMasterVS hlsl { source lightmaster.hlsl target vs_3_0 entry_point multiTypeLightVS preprocessor_defines lightCount=3 default_params { param_named_auto worldViewProj_m worldviewproj_matrix param_named_auto world_m world_matrix param_named_auto cameraPos camera_position_object_space param_named_auto lightPoses light_position_object_space_array 3 } } fragment_program lightMasterPS hlsl { source lightmaster.hlsl target ps_3_0 entry_point multiTypeLightPS preprocessor_defines lightCount=3 default_params { param_named_auto lightPoses light_position_object_space_array 3 param_named_auto lightDirs light_direction_object_space_array 3 param_named_auto SLParamsArray spotlight_params_array 3 param_named_auto diffColors light_diffuse_colour_array 3 param_named_auto specColors light_specular_colour_array 3 param_named_auto lightAttens light_attenuation_array 3 param_named_auto lightDists light_distance_object_space_array 3 param_named_auto ambientColor ambient_light_colour param_named specShine float 50 } } material lightMasterA { technique { pass { vertex_program_ref lightMasterVS {} fragment_program_ref lightMasterPS {} } } }
the HLSL file:
struct vertexIn { float4 position : POSITION; float3 normal : NORMAL0; }; struct vertexOut { float4 position : POSITION; float3 normal : TEXCOORD0; float3 viewDir : TEXCOORD1; float3 pixelToLight[lightCount] : TEXCOORD2; }; float attenuation(float lightDist, float4 lightAtten) { float luminosity = 0; luminosity= 1 / ( lightAtten.y + lightAtten.z*lightDist + lightAtten.w*pow(lightDist,2)); return luminosity; } //point light sub pixel program //-------------------------------------------------------------------------------- void pointLightPS( float3 iNormal, float3 iViewDir, float3 iPixelToLight, float4 diffColor, float4 specColor, float4 lightAtten, float lightDist, float specShine, inout float4 diff, inout float4 spec ) { if( lightAtten.x > lightDist) { float luminosity = attenuation(lightDist, lightAtten); float dotNL = dot ( iPixelToLight, iNormal ); float3 halfAng = normalize(iViewDir + iPixelToLight); float dotNH = dot(iNormal, halfAng); spec += pow(saturate(dotNH),specShine) * specColor * luminosity; diff += (saturate(dotNL)) * diffColor * luminosity; } } //-------------------------------------------------------------------------------- //directional light sub pixel program //-------------------------------------------------------------------------------- void directionalPS( float3 iNormal, float3 iViewDir, float3 iPixelToLight, float4 diffColor, float4 specColor, float specShine, inout float4 diff, inout float4 spec ) { float dotNL = dot(iPixelToLight, iNormal); float3 halfAng = normalize(iViewDir + iPixelToLight); float dotNH = dot(iNormal, halfAng); diff += saturate(dotNL) * diffColor; spec += pow(saturate(dotNH),specShine) * specColor; } //-------------------------------------------------------------------------------- //spotlight sub pixel program //-------------------------------------------------------------------------------- void spotlightPS( float3 iNormal, float3 iViewDir, float3 iPixelToLight, float3 iSpotLightDir, float4 spotLightParams, float4 diffColor, float4 specColor, float4 lightAtten, float lightDist, float specShine, inout float4 diff, inout float4 spec ) { if( lightAtten.x > lightDist) { float dotPLd = dot(-iPixelToLight, iSpotLightDir); float dotNL = dot(iPixelToLight, iNormal); float luminosity = attenuation(lightDist, lightAtten); if(dotNL > 0) { //diffuse //------------------------------ if ( dotPLd > spotLightParams.y ) diff += dotNL * (1-(spotLightParams.x - dotPLd)/(spotLightParams.x - spotLightParams.y)) * diffColor * luminosity; else if ( dotPLd > spotLightParams.x ) diff += dotNL * diffColor * luminosity; //------------------------------ // specular //------------------------------ if (dotPLd > 0) { float3 halfAng = normalize(iViewDir + iPixelToLight); float dotNH = dot(iNormal, halfAng); spec += pow(saturate(dotNH),specShine) * specColor * luminosity; } //------------------------------ } } } //-------------------------------------------------------------------------------- // main vertex program //-------------------------------------------------------------------------------- vertexOut multiTypeLightVS( vertexIn input, uniform float4x4 worldViewProj_m, uniform float4x4 world_m, uniform float4 cameraPos, uniform float4 lightPoses[lightCount] ) { vertexOut output= (vertexOut)0; output.position = mul(worldViewProj_m, input.position); output.normal = mul(world_m, input.normal); output.viewDir = cameraPos - input.position; for(int i = 0; i < lightCount; i++) { // if the light is not empty if( !(lightPoses[i].x==0 && lightPoses[i].y==0 && lightPoses[i].z==0 && lightPoses[i].w==0) ) output.pixelToLight[i] = lightPoses[i] - input.position; } return output; } //-------------------------------------------------------------------------------- //main pixel program //-------------------------------------------------------------------------------- float4 multiTypeLightPS( vertexOut input, uniform float4 lightPoses[lightCount], uniform float4 SLParamsArray[lightCount], uniform float3 lightDirs[lightCount], uniform float4 diffColors[lightCount], uniform float4 specColors[lightCount], uniform float4 lightAttens[lightCount], uniform float4 lightDists[lightCount], uniform float4 ambientColor, uniform float specShine ) : COLOR { input.viewDir = normalize( input.viewDir ); input.normal = normalize( input.normal ); float4 diff = float4(0, 0, 0, 0); float4 spec = float4(0, 0, 0, 0); for(int i = 0; i<lightCount ; i++) { input.pixelToLight[i] = normalize( input.pixelToLight[i] ); // if the light position data is (0,0,0,0),the light is empty if( !(lightPoses[i].x==0 && lightPoses[i].y==0 && lightPoses[i].z==0 && lightPoses[i].w==0) ) { if(lightPoses[i].w==0) { // if the light is not empty and the w component is 0, we have a directional directionalPS( input.normal, input.viewDir, lightPoses[i].xyz, diffColors[i], specColors[i], specShine, diff, spec); } else if ( SLParamsArray[i].x==1 && SLParamsArray[i].y==0 && SLParamsArray[i].z==0 && SLParamsArray[i].w==1 ) { // if the light is not directional and the spot light params is (1,0,0,1), we have a point light pointLightPS( input.normal, input.viewDir, input.pixelToLight[i], diffColors[i], specColors[i], lightAttens[i], lightDists[i], specShine, diff, spec); } else { // otherwise, we have a spotlight spotlightPS( input.normal, input.viewDir, input.pixelToLight[i], normalize(lightDirs[i]), SLParamsArray[i], diffColors[i], specColors[i], lightAttens[i], lightDists[i], specShine, diff, spec); } } } return ambientColor + diff + spec ; } //--------------------------------------------------------------------------------
My shader in action; red directional, blue point light from below and white spotlight from the left.